In the manufacture of circuit boards and wiring boards it has been traditional to solder coat or solder wet surfaces on components, boards and the like before assembly. The reason for solder coating or, in some cases, tin or lead electroplating followed by fusing of surfaces, has been to preserve the solderability for long periods of time. Thus, when surfaces on components or boards have been solder coated, the coated surfaces are able to be solder joined without further treatment. Throughout the attached specification the term "element" has been used to mean circuit boards, wiring boards, or any components that have surfaces, holes, pins or the like that are to be solder joined.
Copper circuit boards or wiring boards are cheaper to produce than those that are solder coated, but they do not retain their solderability properties very long because the copper oxidizes rapidly after etching. (Etching is carried out to clean copper surfaces prior to soldering.) Protective coatings are sometimes applied to bare copper surfaces to preserve their solderability. These protective coatings are applied by dip coat or spray to exclude oxygen from the surfaces therefore retaining the solderability of the copper surfaces. Some protective coatings include a small amount of mild rosin flux, and during soldering, the alcohol component of the rosin flux dissolves the protective coating off the copper surfaces and permits the flux to activate the copper for good wave soldering results. When a water soluble flux is to be used for soldering, then rosin protective coatings on copper surfaces cannot be used because they are not compatible either with water soluble flux or with water cleaning after wave soldering. Commercial protective coatings have been formulated based on imidiazole and benzotriazole for use with water soluble flux. When a water soluble flux contacts the surface to be soldered on the circuit board, it penetrates these passivating protective materials based on imidiazole or benzotriazole on a copper surface and permits excellent wave soldering results.
Bare copper surfaces for fine-pitch surface mount components are preferred because of lower cost and flatness of the pads compared to other coatings. However, the protective coatings required for copper surfaces add additional costs to the preparation of surfaces for soldering and consequently to board fabrication. Normal fluxes that are applied to surfaces that have been coated either by oxides or protective coatings dissolve these coatings from the boards. However, flux residues and the removed oxides remain on these surfaces and are carried through a preheating stage prior to soldering. It has been found that some of the flux residues and removed oxides interfere with automatic pin testing and in some cases have to be removed by cleaning to prevent other problems occurring including corrosion of the solder connections.
Traditional surface coating treatments for preserving solderability of surfaces on circuit boards and the like generally still require the use of flux in order to properly prepare the surfaces of the leads and terminations of the components mounted in holes on the circuit boards or surface mount devices on the circuit surfaces prior to and during production wave soldering. The major ingredient of most traditional fluxes is alcohol and alcohol is the carrier which moves the activator part of the flux to coat the surfaces of boards and assist in removing metal surface oxides prior to wave soldering. Alcohols evaporate from the fluxer during production and also after being applied to the circuit board. Alcohol generally evaporates in a wave soldering machine during the preheating stage and these evaporated alcohols are called "volatile organic compounds" and must be exhausted from the machine out of the building. Volatile organic compounds are generally considered undesirable to the environment as they may lead to, or cause, pollution and/or global warming.
It has recently been suggested that oxides and coatings may be removed from circuit boards, component leads and terminations of components by electrochemical reduction treatment which eliminates the need for flux and specifically a flux containing alcohol. The electrochemical reduction treatment liquid removes the oxides and restores the solderability of the surfaces to be solder joined on the board and component leads.